1. Field of the Invention
The present invention relates to double block and bleed valve systems and, more particularly, to a bleed valve assembly for use in such a system.
2. Description of the Background
In industries which produce liquid products, particularly beverage industries, such as breweries, soft drink bottlers, dairies, etc., large networks of pipes are used to transfer liquid from one place to another. In these networks of pipes, the problem of contamination is an ever present risk. Accordingly, it is essential to provide means for internal cleaning of the pipe work at regular intervals. It will be recognized that because of the complexity of the pipe networks, any attempts to try cleaning by dismantling the networks is time consuming, expensive, and will result in significant downtime of the facility.
To overcome some of the cleaning problems associated with complex networks of pipes, valve isolating systems are employed. Such valve isolating systems, in and of themselves, present a problem inasmuch as there are normally dead spaces in the vicinity of the valve which cannot be readily cleaned because of their inaccessibility. Moreover, many such valve isolating systems do not provide any protection against leakage of cleaning fluids from one part of the pipe work on one side of the valve isolation system to another part on the other side which still contains liquid food material which, as a result, could become seriously contaminated.
In U.S. Pat. No. 4,458,706, there is disclosed a double block and bleed valve system which utilizes three butterfly valves in a T-network, two of the butterfly valves serving as the double block valves, the third butterfly valve serving as a drain valve for the chamber formed between the two block valves. The system further includes a so-called "clean-in-place" feature which comprises a spray head which is disposed in the chamber through which can be introduced a cleaning fluid such that the chamber can be thoroughly cleaned and the spent cleaning fluid removed through the drain or bleed valve without having to dismantle the block valves.
In the system disclosed in the aforementioned patent, the chamber formed between the two block valves comprises a T-construction with the result that the flowway defined by the chamber does not have a generally smooth, uninterrupted flowway surface which is desirable to avoid turbulent flow. Moreover, because the surface is discontinuous due to the T-construction, the chamber is more difficult to clean.